Blue Planet II is a 2017 British nature documentary series on marine life produced by the BBC Natural History Unit. Like its predecessor, The Blue Planet (2001), it is narrated and presented by naturalist Sir David Attenborough.After being announced in 2013, filming took four years in 39 countries over more than 125 international trips. The musical score was composed by Hans Zimmer, Jacob Shea and David Fleming, and English rock band Radiohead reworked their 2011 song "Bloom" with Zimmer specifically for the series.

The series debuted on 29 October 2017 and was simultaneously cast on BBC One, BBC One HD and BBC Earth, making it the first natural history series to premiere on the same day in the United Kingdom, Nordic regions, Europe and in Asia. In the United States, the series premiered on January 20, 2018, as part of a five-network simulcast on BBC America, AMC, IFC, Sundance, and WE tv.

The series received almost universal critical acclaim. It had the highest viewing figures of any television programme in the United Kingdom during 2017, and was so widely watched in China that it reportedly caused internet issues. It was credited with increasing public and political interest in issues affecting marine life, in particular marine plastic pollution, which was dubbed "the Blue Planet effect".